1. Technical Field
The present invention relates to an input apparatus having a capacitive touch sensor.
2. Related Art
There is known a capacitive touch sensor (types thereof including a touch panel, a touch pad, and a touch switch) that detects a touch of a user's finger by detecting a change in capacitance (for example, see JP-A-2008-52583). This type of touch sensor is used for, for example, an operation panel of the housing of an electronic device, and allows the electronic device to be operated, as an input apparatus which receives a user's manual input.
Specifically, the touch sensor includes, for example, a pad configured to detect and output a capacitance; and a controller (e.g., a control IC) configured to detect a change in the capacitance outputted from the pad and to output the detected change to a CPU or the like. For example, the controller converts a signal outputted from the pad into a CPU processable signal (for example, a value indicating an electric potential, or a frequency), and outputs the CPU processable signal.
The characteristics of individual electronic devices, pads and controllers vary depending on the model. Accordingly, when a minute change in capacitance is detected, the characteristics of an individual device have a significant influence on the detected change, thus a variation occurs in the values measured by respective controllers of electronic devices.
In order to prevent a malfunction of the electronic device such as an inability to detect a touch due to the occurrence of a variation, a touch sensor, after being attached to the electronic device, is adjusted in the process of manufacturing the electronic device. In the adjustment of the touch sensor, an output value of the pad is measured, for example, in a state (OFF state) where a user's finger or other object is not close to or in contact with a pad, and a correction value (for example, a correction value for adjusting the gain) is calculated, with which the measured value can be corrected to a predetermined reference value (a proper value for determination of the OFF state), and is stored in a nonvolatile memory or the like. Subsequently, correction (for example, the gain adjustment) of the output of the pad is made based on the correction value by the processing of at least one of the control IC and the CPU, so that an appropriate value is measured.
However, in the process of manufacturing electronic devices, a user's finger, a tool, or an other object may approach or come into contact with a pad during the adjustment of a touch sensor, thus an accurate measurement value cannot be obtained properly. Thus, an appropriate correction value cannot be obtained, and consequently, a malfunction of the touch sensor is caused.